This article is in the Features category, and was posted on 14/11/2002.

Step by step: the making of a chainring (Author: Anders)

The Machinist

Step by step: the making of a chainring

This was meant to be a project, that could be done over the summer,
but here in Denmark we have had one of the best summers in a long time,
so it has taken a bit longer than expected.

The rings are made on a FADAL 2016 '99 model with the old 88 control.
This is a CNC milling machine with a maximum speed of 7500 rpm.

For anybody interested, the CAD/CAM used here is SolidWorks/CAMWorks.

The CAD/CAM work could be done in about 2-3 hours if one could stay
indoors for that long!! The process pictured is the making of a 42T
5-arms design. It’s a long process to implement it at first, but when
it’s all in place, it goes pretty fast. When it is all optimized it
will takes about 15-20 minutes to make one of these chainring.

The Aluminium used is 7075 T6 heat treated 4 mm alloy plates,
these are very precise with almost no warp.

The chainrings are not made for sale!

The first thing to be done, was making a fixture for the Aluminium plate.
This is made of 20 mm thick Aluminium:

Here the topside of the tool is finished:

The plate will be fixated to the Aluminium tool with normal chainring bolts:

Next we start out with a square aluminium plate:

The holes are being made for the bolts, and then it is fixed in the tool made in the start:

The plate is bolted to the tool:

Here is the picture off the chainring drawed in SolidWorks:

Now we start making the teeth:

Now the topside of the chainring is finished:

Now the other side of the chainring can be made.
This will be implemented in the CNC milling machine, so there will be no need to use this machine:

The teeth has to be cut in angle, so the chain can't "ride" on the teeth, but instead fall into place.
On this picture you can also see, that the inside edges of the chainring has been cut in an angle of 45° to reduce weight.

Here it is compared with a T.A. Specialites chain ring.

You can see, that your design is much smaller in profile, and therefore lighter. The shifting ramps are also different.

Our new design is very light, only 58 grams with 4 hardsteel shifting ramps:

The ring seen on the picture, has been tested in very muddy conditions,
on our 26 km home trail. It performed flawlessly, no shifting problems and no chainsuck.

The future modifications will include a design, so that the shifting ramps may not be needed.
It's a special 45° cutting on the back, that acts like a shiftingramp going all the way around the chainring.
Finally they will be anodized black.

We will also round the edges some more and optimize the design of the holes. This may result in a weight under 50 grams.

UPDATE:

We have shaved of some more material and removed the shifting ramps,
so now the weight is down to 56 grams for the 42T. We have also made a
32T middle ring, and that weighs 34 grams. We are going to make a bit more
milling to the edges of the chainring, which should save about 2 grams more.

We have made a custom tool, for the process of cutting the teeths in angle, so
there's no more need to use the green machine, shown in the pictures above. The
CNC milling machine can now make the whole chainring in one process. It takes about
13 min to make a 42T and about 8 min for a 32T.

The new design with bigger holes and rounded edges:

UPDATE:

We have made a new 30T chainring type for our 2x9 setup.

It weighs only 25 grams, which is 5 grams lighter than a 30T TA Specialites ring.

The chainring set is now down to 80 grams. That is 16% lighter than TA Specialites.